Measuring with the Gauge
43
A GUIDE TO SOUND VELOCITIES
Table of Sound Velocities
¾ Velocities can vary according to the precise grade and processing conditions.
This table is included as a guide only.
Wherever possible, the Gauge should always be calibrated on the material under test.
¾ These Velocities are given in good faith and are believed to be accurate within the limits
described above.
No liability is accepted for errors.
¾ Velocities given are the compressional wave velocity c
l
.
Reading Conversion
In some circumstances it may not be possible to Calibrate the Gauge :
Ö If there is no test-sample available for the Material which is to be measured
Ö And : if the Velocity of Sound for the Material to be measured is not currently known
To allow uncalibrated measurements to be made, use this procedure :
¾ When measuring :
the Gauge should be initially calibrated for Mild Steel, by selecting Mild Steel from the
Materials List - see : Calibration by Named Material
, page 36
¾ Later, when preparing a report :
Ö Choose the actual material from the Table of Sound Velocities, or otherwise find out
the Velocity of Sound
Ö convert the readings by multiplying each reading by by the Conversion Factor for
the material being measured - see : Table of Sound Velocities,
page 44
Example – if the Gauge is calibrated for Mild Steel [5920 m/s], and a reading is being taken
on Copper [4700 m/s] :
T = t x V
COPPER
/ V
STEEL
= t x 4700 / 5920 = t x 0.794
thus : T = t x f
where : T = true thickness of Copper being measured
t = actual reading obtained
f = Conversion Factor
V
COPPER
= Sound Velocity in Copper : 4700 m/s
V
STEEL
= Sound Velocity in Steel : 5920 m/s
Conversion Factor f :
¾ Conversion Factor is given for various materials in the Table of Sound Velocities,
page
44
¾ If the Material does not appear in the Table, but the Velocity of Sound, V
MATERIAL,
is
known for the Material : calculate conversion factor, f = V
MATERIAL
/
V
STEEL
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